Pyrolysis system and method of pyrolyzing waste plastics

Abstract

The present application relates to waste plastic pyrolysis technical field, disclose a kind of pyrolysis system and waste plastic pyrolysis method.Pyrolysis system includes feeding unit, pyrolysis unit, separation unit and heating unit;Wherein, the feeding unit is used to dry and transport waste plastics;The pyrolysis unit is used to pyrolysis waste plastics from feeding unit and / or from the circulating oil of separation unit, obtain pyrolysis product;The separation unit is used to separate the pyrolysis product, obtain circulating oil, product oil and pyrolysis gas;The heating unit is used to burn the pyrolysis gas, and the feeding unit and pyrolysis unit are heated.The pyrolysis device provided by the present application not only has good sealing, long running cycle, low energy consumption, but also can improve the yield of product oil in waste plastic pyrolysis product, suitable for industrialization promotion.

Description

Technical Field

[0001] This invention relates to the field of waste plastic pyrolysis technology, specifically to a pyrolysis system and a waste plastic pyrolysis method. Background Technology

[0002] The "white pollution" caused by waste plastics is becoming increasingly serious. With the proposal of dual carbon targets, chemical recycling technology for waste plastics is receiving more and more attention.

[0003] Currently, most film-shaped waste plastics are made of PE and PP, and the primary method for chemical recycling of these waste plastics is pyrolysis. The main pyrolysis process at present is rotary kiln technology, which has already achieved industrial application. Other processes, such as fluidized bed pyrolysis, have not yet been industrially applied and remain at the industrial demonstration stage.

[0004] However, rotary kiln technology also has its own drawbacks. First, there is the issue of continuous online decoking. When the external heating jacket is used, the temperature of the inner surface of the kiln body is too high, which can easily lead to excessive cracking of waste plastics and the formation of coke. The coke adheres to the rotary kiln wall, making decoking difficult and preventing long-term operation. It requires periodic shutdowns for decoking. Second, due to the external heating method, the heating area is limited. Rotary kiln pyrolysis often relies on extending the pyrolysis time to ensure a high pyrolysis rate, resulting in a low yield of pyrolysis oil and a high yield of semi-coke and pyrolysis gas. Summary of the Invention

[0005] The purpose of this invention is to solve the above-mentioned technical problems and provide a pyrolysis system and waste plastic pyrolysis method with high heat transfer efficiency, reduced coking rate and increased pyrolysis oil yield.

[0006] To achieve the above objectives, a first aspect of the present invention provides a pyrolysis system, the system comprising a feeding unit, a pyrolysis unit, a separation unit, and a heating unit; wherein the feeding unit is used for drying and transporting waste plastics; the pyrolysis unit is used for pyrolyzing the waste plastics from the feeding unit and / or the circulating oil from the separation unit to obtain pyrolysis products; the separation unit is used for separating the pyrolysis products to obtain circulating oil, product oil, and pyrolysis gas; and the heating unit is used for burning the pyrolysis gas to provide heat to the feeding unit and the pyrolysis unit.

[0007] A second aspect of the present invention provides a method for pyrolyzing waste plastics, the method being carried out in the pyrolysis system described in the first aspect of the present invention, comprising the following steps:

[0008] (1) Dry the waste plastic to obtain dried waste plastic;

[0009] (2) The dried waste plastic is pyrolyzed to obtain pyrolysis products and semi-coke;

[0010] (3) Separate the pyrolysis products to obtain circulating oil, product oil and pyrolysis gas;

[0011] (4) Combust the pyrolysis gas to obtain high-temperature flue gas; wherein the high-temperature flue gas is returned to the heat source for drying and pyrolysis reactions in steps (1) and (2);

[0012] Optionally (5), the circulating oil is recycled back to step (2).

[0013] Through the above technical solution, the pyrolysis device provided by the present invention not only has good sealing performance, long operating cycle and low energy consumption, but also can improve the yield of circulating oil and product oil in waste plastic pyrolysis products, especially the yield of product oil, and is suitable for industrial promotion. Attached Figure Description

[0014] Figure 1 This is a pyrolysis system diagram of a preferred embodiment provided in this invention;

[0015] Explanation of reference numerals in the attached figures

[0016] 1. Material pit; 2. Primary bucket elevator; 3. Primary silo.

[0017] 4. Secondary bucket elevator; 5. Secondary hopper; 6. Discharge screw conveyor

[0018] 7. Pyrolysis reactor 71, reactor shell 72, hollow stirring shaft

[0019] 73. Spiral blade; 74. Sealing structure; 75. Expansion joint

[0020] 8. Primary separation unit; 9. Secondary separation unit; 10. Combustion boiler

[0021] 11. Fan Detailed Implementation

[0022] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0023] A first aspect of the present invention provides a pyrolysis system, the system comprising a feeding unit, a pyrolysis unit, a separation unit, and a heating unit; wherein the feeding unit is used for drying and transporting waste plastics; the pyrolysis unit is used for pyrolyzing the waste plastics from the feeding unit and / or the circulating oil from the separation unit to obtain pyrolysis products; the separation unit is used for separating the pyrolysis products to obtain circulating oil, product oil, and pyrolysis gas; and the heating unit is used for burning the pyrolysis gas to provide heat to the feeding unit and the pyrolysis unit.

[0024] In a preferred embodiment, the feeding unit includes a material pit 1, a primary bucket elevator 2, a primary silo 3, a secondary bucket elevator 4, a secondary silo 5, and a discharge screw conveyor 6 connected in sequence. The discharge screw conveyor 6 is connected to the pyrolysis unit. The material pit 1 is used to store waste plastics; the primary bucket elevator 2 is used to transport the waste plastics from the material pit 1 to the primary silo 3; the secondary bucket elevator 4 is used to transport the waste plastics from the primary silo 3 to the secondary silo 5; and the discharge screw conveyor 6 is used to transport the waste plastics from the secondary silo 5 to the pyrolysis unit. Figure 1 As shown.

[0025] In a preferred embodiment, the storage pit 1 is an open or semi-open storage device. That is, in this invention, the storage pit 1 can be an open device.

[0026] In a preferred embodiment, the outer shells of the primary bucket elevator 2 and the secondary bucket elevator 4 are provided with flue gas heating jackets, which are connected to the pyrolysis unit.

[0027] In this invention, high-temperature flue gas from the pyrolysis unit at a temperature of 120-180°C is used to heat the primary and secondary bucket elevators, which can heat the waste plastics to 80-120°C, preferably 100-110°C, thereby drying the waste plastics while transporting them.

[0028] In a preferred embodiment, cooling jackets are provided outside the motor drive shafts of the primary bucket elevator 2 and the secondary bucket elevator 4. These cooling jackets are used to cool the motors to prevent the dry heat from the primary and secondary bucket elevators 2 and 4 from being conducted to the motors and causing damage. The present invention does not specifically limit the cooling medium in the cooling jackets; the cooling medium can be air, water, or heat transfer oil.

[0029] In a preferred embodiment, the primary bucket elevator 2 is sealed to the primary silo 3, and the secondary bucket elevator 4 is sealed to both the primary silo 3 and the secondary silo 5.

[0030] In a preferred embodiment, the primary silo 3 and the secondary silo 5 are sealed storage devices equipped with vents; the sealing prevents water vapor from spreading arbitrarily, while the vents are used to discharge water vapor generated during the transportation of waste plastics. The discharged water vapor is condensed and sent to a wastewater treatment plant for treatment to meet standards before being discharged.

[0031] In a preferred embodiment, heat-insulating jackets are provided outside the primary silo 3 and the secondary silo 5. In this invention, the heat-insulating jackets further enhance the drying effect of waste plastics.

[0032] In a preferred embodiment, a stirring spiral is provided inside the secondary silo 5, and the bottom of the secondary silo 5 is a conical head with a cone angle of 30-120°, preferably 45-60°. In this invention, setting the cone angle of the conical head between 30-120° avoids bridging and enables rapid material discharge.

[0033] In a preferred embodiment, the discharge screw conveyor 6 is selected from an extruder and / or a slag extruder, and is located below the secondary silo 5. In this invention, the physical seal between the secondary silo and the pyrolysis unit is achieved through the mechanical pressure generated during the material conveying process of the extruder or slag extruder.

[0034] In a preferred embodiment, the pyrolysis unit includes a pyrolysis reactor 7, wherein the pyrolysis reactor includes a reactor shell 71, a hollow stirring shaft 72, a spiral blade 73, and a sealing structure 74; wherein the hollow stirring shaft 72 penetrates the reactor shell 71, and a hollow pipe for introducing high-temperature flue gas is provided in the hollow stirring shaft 72; the spiral blade 73 is disposed on the hollow stirring shaft 72, and the sealing structure 74 is used to seal the connection between the hollow stirring shaft (72) and the reactor shell (71) and the inlet and outlet of the hollow pipe.

[0035] In this invention, the outer shell of the pyrolysis reactor is fixed, while the hollow stirring shaft drives the spiral blades to rotate continuously within the reactor shell, agitating the waste plastic entering the pyrolysis reactor. High-temperature flue gas at 600-800°C from the heating unit is introduced into the hollow tube of the hollow stirring shaft, heating the pyrolysis reactor to 400-700°C, preferably 450-550°C, to heat the pyrolysis reaction. Sealing structures are provided at the connection between the outer shell and the hollow stirring shaft, and at the connection between the inlet and outlet of the hollow stirring shaft tube and the flue gas pipe connected to the same hollow tube, to improve the sealing performance between the static and dynamic components. This invention does not impose any special limitations on the sealing structure; any sealing structure conventionally used between static and dynamic components in the art can be used in this invention.

[0036] In a preferred embodiment, the reactor shell 71 is provided with a feed inlet, a discharge outlet, and a gas outlet. The feed inlet is connected to the discharge screw conveyor 6 and is used to feed waste plastics; the discharge outlet is used to discharge the semi-coke generated during the pyrolysis reaction; and the gas outlet is connected to the separation unit and is used to transport the pyrolysis products generated during the pyrolysis reaction to the separation unit.

[0037] In a preferred embodiment, the hollow stirring shaft 72 is coaxially arranged with the reactor shell 71.

[0038] In a preferred embodiment, the outer diameter of the hollow stirring shaft 72 is at least four times the size of the waste plastic particles, preferably five to seven times. In this invention, limiting the outer diameter of the hollow stirring shaft to be larger than the size of the waste plastic particles prevents the waste plastic from entangled in the hollow stirring shaft, thus preventing operational malfunctions.

[0039] In a preferred embodiment, the helical blade 73 is provided with vent holes, the diameter of which is ≤10mm. In this invention, providing vent holes on the helical blade helps to promote the discharge of pyrolysis products and the flow of circulating oil.

[0040] In a preferred embodiment, the distance between the outermost edge of the spiral blade 73 and the reactor shell 71 is 5-20 mm; the spiral spacing between adjacent spiral blades 73 is greater than the particle size of the waste plastic.

[0041] In a preferred embodiment, the hollow stirring shaft 72 and the end caps of the reactor shell 71 are made of different materials, with the thermal expansion coefficient of the hollow stirring shaft 72 being greater than that of the end caps of the reactor shell 71. In this invention, the self-sealing of the rotating equipment is achieved between the hollow stirring shaft and the end caps of the reactor shell through a temperature difference.

[0042] In a preferred embodiment, the pyrolysis reactor further includes an expansion joint 75, which is disposed outside the sealing structure 74. In this invention, the number of expansion joints is the same as the number of sealing structures. The coupling between the expansion joints and the sealing structures prevents the leakage of high-temperature flue gas from the empty pipe due to deformation caused by thermal expansion and contraction.

[0043] In a preferred embodiment, the separation unit includes a multi-stage condensation separation device, wherein each stage of the condensation separation device includes a condenser and a separator.

[0044] In this invention, the separation unit processes the pyrolysis products from the pyrolysis reactor, separating them into circulating oil, product oil, and pyrolysis gas. It should be noted that this invention does not impose a specific limitation on the separation order of the pyrolysis products. The pyrolysis products can be first separated into liquid-phase pyrolysis oil and gaseous-phase pyrolysis gas, and then the liquid-phase pyrolysis oil can be further separated into circulating oil and product oil; alternatively, the pyrolysis products can be first separated into circulating oil and residual components, and then the residual components can be separated into product oil and pyrolysis gas. Furthermore, the product oil in this invention can be further processed according to actual needs. This invention does not impose a specific limitation on the cutting distillation range of the product oil; the product oil can be separated according to actual requirements. To achieve the desired condensation effect, the condenser in each stage of the condensation separation device can be a single unit or multiple units connected in series.

[0045] In a preferred embodiment, the separation unit includes a two-stage condensation separation device, wherein the first-stage separation device (8) is used to separate circulating oil with a boiling point ≥180℃; and the second-stage separation device (9) is used to separate pyrolysis gas to obtain product oil. Herein, pyrolysis gas in this invention has a well-known meaning in the art, and product oil is the remaining component after the pyrolysis gas has been separated.

[0046] In this invention, the pyrolysis products first enter a primary separation unit to separate circulating oil with a boiling point ≥180℃. This circulating oil can be returned, in whole or in part, to the pyrolysis reactor via a discharge screw conveyor 6. Returning the circulating oil to the pyrolysis reactor prevents coking of the waste plastics during pyrolysis and allows for further pyrolysis of the heavier components in the pyrolysis products, breaking them down into lighter components. The remaining portion enters a secondary separation unit for further separation, yielding pyrolysis gas and product oil. The separated product oil is stored in a product oil storage tank, while the remaining pyrolysis oil and gas are sent to a heating unit.

[0047] In a preferred embodiment, the heating unit includes a gas-fired boiler 10 and a fan 11. One end of the fan 11 is connected to a separation unit, and the other end is connected to the gas-fired boiler 10, for conveying pyrolysis gas from the separation unit to the gas-fired boiler 10. The gas-fired boiler 10 is also sequentially connected to a pyrolysis reactor 7, a secondary bucket elevator 4, and a primary bucket elevator 2. The gas-fired boiler 10 is used to burn the pyrolysis oil and gas to obtain high-temperature flue gas, which is then sequentially conveyed to the pyrolysis reactor 7, the secondary bucket elevator 4, and the primary bucket elevator 2. In this invention, the high-temperature flue gas undergoes heat exchange in the primary bucket elevator and is then treated to meet emission standards before being discharged through the chimney.

[0048] In a preferred embodiment, the fan 10 is a variable frequency fan, wherein a pressure transmitter is provided between the variable frequency fan and the pyrolysis reactor 7, and the variable frequency fan and the pyrolysis reactor 7 are pressure-interlocked through the pressure transmitter.

[0049] In this invention, when the pressure of the pressure transmitter is between a vacuum of 35 Pa and a gauge pressure of 50 Pa, the variable frequency fan is started. This ensures that the pyrolysis oil and gas do not escape and that no air enters the pyrolysis reactor.

[0050] A second aspect of the present invention provides a method for pyrolyzing waste plastics, wherein the method includes the following steps:

[0051] (1) Dry the waste plastic to obtain dried waste plastic;

[0052] (2) The dried waste plastic is pyrolyzed to obtain pyrolysis products and semi-coke;

[0053] (3) Separate the pyrolysis products to obtain circulating oil, product oil and pyrolysis gas;

[0054] (4) Combust the pyrolysis gas to obtain high-temperature flue gas; wherein the high-temperature flue gas is returned to the heat source for drying and pyrolysis reactions in steps (1) and (2);

[0055] Optionally (5), the circulating oil is recycled back to step (2).

[0056] In a preferred embodiment, the drying includes primary drying and secondary drying, wherein the drying temperatures of the primary drying and secondary drying are each individually selected from 80-120°C, preferably 100-110°C.

[0057] In a preferred embodiment, the temperature of the pyrolysis reaction is 400-700℃, preferably 450-550℃; the pyrolysis reaction time is 10-60 min, preferably 30-50 min.

[0058] In a preferred embodiment, the separation includes primary separation and two-stage separation. The pyrolysis products are first subjected to primary separation to obtain circulating oil; the remaining part is further subjected to secondary separation to obtain product oil and pyrolysis gas; wherein the boiling point of the circulating oil is ≥180℃.

[0059] In a preferred embodiment, at least a portion of the recycled oil is returned to the pyrolysis reaction; wherein the mass ratio of the recycled oil returned to the pyrolysis reaction to the waste plastic is 1:0.5-5, preferably 1:0.5-2.

[0060] In a preferred embodiment, the method is carried out in the pyrolysis system described in the first aspect of the invention.

[0061] The present invention will be described in detail below through embodiments.

[0062] The pyrolysis system in the embodiment is as follows Figure 1 As shown: The system includes a feeding unit, a pyrolysis unit, a separation unit, and a heating unit. The feeding unit comprises a material pit 1, a primary bucket elevator 2, a primary silo 3, a secondary bucket elevator 4, a secondary silo 5, and a discharge screw conveyor 6. The material pit 1 is a semi-open storage device, while the primary silo 3 and secondary silo 5 are closed storage devices equipped with air outlets and insulation jackets. The bottom of the secondary silo 5 is a conical head with a cone angle of 60°, and an internal stirring screw is installed. Both the primary bucket elevator 2 and the secondary bucket elevator 4 have flue gas heating jackets on their outer shells, and cooling jackets with air as the cooling medium are installed outside the motor drive shafts. The primary bucket elevator 2 is sealed to the primary silo 3, and the secondary bucket elevator 4 is sealed to both the primary silo 3 and the secondary silo 5. The discharge screw conveyor 6 is located below the secondary silo 5 and is an extruder equipped with a circulating oil inlet.

[0063] The pyrolysis unit includes a pyrolysis reactor 7, which comprises a reactor shell 71, a hollow stirring shaft 72, spiral blades 73, a sealing structure 74, and an expansion joint 75. The reactor shell 71 has a waste plastic inlet, a semi-coke outlet, and a pyrolysis product outlet. The hollow stirring shaft 72 penetrates the reactor shell and is coaxially arranged with the reactor shell 71. A hollow pipe for introducing high-temperature flue gas is installed within the hollow stirring shaft 72. The outer diameter of the hollow stirring shaft is 150 mm, and the material of the hollow stirring shaft is 316L. The connection between the hollow stirring shaft and the reactor shell, as well as the inlet and outlet of the hollow pipe, are sealed by the sealing structure 74 and the expansion joint 75. The spiral blades 73 are mounted on the hollow stirring shaft 72 and have 8 mm diameter vent holes. The distance between the outermost edge of the spiral blades 73 and the reactor shell 71 is 5 mm, and the spiral spacing of the spiral blades 73 is 40 mm. The hollow stirring shaft 72 and the reactor shell 71 achieve self-sealing through temperature difference and the difference in the expansion coefficients of the materials.

[0064] The separation unit includes two stages of condensation separation devices connected in sequence. The first stage separation device 8 includes a first stage condenser and a first stage separator; the second stage separation device 9 includes a second stage condenser and a second stage separator; the first stage condenser is connected to the outlet of the pyrolysis product in the pyrolysis reactor, the first stage separator is connected to the circulating oil inlet of the feed screw conveyor 6, and the second stage separator is connected to the product oil storage tank.

[0065] The heating unit includes a gas boiler 10 and a variable frequency fan 11. The gas boiler 10 is connected to a secondary separator. One end of the variable frequency fan 11 is connected to the pyrolysis gas outlet of the secondary separator, and the other end is connected to the gas boiler 10. A pressure transmitter is installed between the variable frequency fan 11 and the pyrolysis reactor 7. The variable frequency fan and the pyrolysis reactor 7 are pressure-interlocked through the pressure transmitter. When the pressure of the pressure transmitter is a vacuum of 25 Pa, the variable frequency fan is started.

[0066] The waste plastics in the examples and comparative examples are clean PE films crushed to about 20 mm.

[0067] Example 1

[0068] 1) The waste plastic is placed in the pit. After being dried during the transportation process of the first-stage bucket elevator, the first-stage silo, the second-stage bucket elevator, and the second-stage silo, the waste plastic is transported to the pyrolysis reactor by the discharge screw conveyor. The drying temperature of the first-stage bucket elevator is 105℃, and the drying temperature of the second-stage bucket elevator is 110℃.

[0069] 2) The dried waste plastics are pyrolyzed in a pyrolysis reactor to obtain semi-coke and pyrolysis products; the reaction temperature of the pyrolysis reactor is 450℃, and the stirring screw speed is adjusted so that the average residence time of the waste plastics in the pyrolysis reactor is 30min.

[0070] 3) The pyrolysis products enter the primary condenser, where the condensation temperature is 180℃. Circulating oil with a boiling point ≥180℃ is separated from the primary separator, and the remaining portion enters the secondary condenser. The condensation temperature of the secondary condenser is 28℃, where product oil with a boiling point <180℃ and pyrolysis gas are separated from the secondary separator. The circulating oil and waste plastics are recycled back to the pyrolysis reactor at a mass ratio of 1:1.

[0071] 4) The pyrolysis gas enters the combustion boiler for combustion to obtain high-temperature flue gas; when the vacuum degree of the pressure transmitter is 25Pa, the variable frequency fan is started, and the high-temperature flue gas is sequentially transported by the variable frequency fan to the pyrolysis reactor, the secondary bucket elevator and the primary bucket elevator as a heat source.

[0072] Example 2

[0073] Similar to Example 1, the difference is that in step (3), the condensation temperature of the first-stage condenser is 350°C, and the circulating oil with a boiling point ≥350°C is separated from the first-stage separator, with the remaining part entering the second-stage condenser; the condensation temperature of the second-stage condenser is 28°C, and the product oil with a separation distillation range of IBP-350°C and pyrolysis gas are separated from the second-stage separator; the obtained circulating oil with a boiling point ≥350°C and waste plastic are recycled back to the pyrolysis reactor in a mass ratio of 1:1.

[0074] Example 3

[0075] Similar to Example 1, except that in step (3), the circulating oil is not returned to the pyrolysis reactor, but sent to the circulating oil storage tank.

[0076] Comparative Example 1

[0077] 1) The waste plastic is placed in the pit. After being dried during the transportation process of the first-stage bucket elevator, the first-stage silo, the second-stage bucket elevator and the second-stage silo, the waste plastic is transported to the pyrolysis reactor by the screw conveyor. The drying temperature of the first-stage bucket elevator is 105℃ and the drying temperature of the second-stage bucket elevator is 110℃.

[0078] 2) The dried waste plastics are pyrolyzed in a rotary kiln to obtain semi-coke and pyrolysis products; to ensure complete pyrolysis, the reaction temperature of the pyrolysis reactor is 550℃; to prevent leakage, the pyrolysis pressure is set to a vacuum of 25Pa.

[0079] 3) The pyrolysis products are condensed with 28°C cooling water, and the resulting pyrolysis oil is sent to the product storage tank; the separated pyrolysis gas is sent to the boiler for combustion and heating as fuel.

[0080] Analysis example 1

[0081] To analyze the pyrolysis products in the comparative examples, pyrolysis products were collected from the pyrolysis product outlets of the pyrolysis reactors in Examples 1-3, respectively. The pyrolysis products were first separated to obtain gaseous pyrolysis gas and liquid pyrolysis oil, and the yield of the pyrolysis gas was calculated. Then, the pyrolysis oil was fractionated to obtain gasoline fractions with a distillation range of 1BP-180℃, diesel fractions with a distillation range of 180-350℃, distillate oils with a distillation range of 350-500℃, and heavy oil fractions with a distillation range of >500℃. Based on the pyrolysis oil, the content of these four fractions was calculated. The pyrolysis products in Comparative Example 1 were analyzed in the same way, and the results are shown in Table 1.

[0082] Table 1

[0083] pyrolysis gas yield 6.1 9.4 12.7 19.2 pyrolysis oil yield 93.4 89.4 85.2 71.2 gasoline fraction 48.2 38.7 31.7 50.1 Diesel fraction 44.6 38.2 45.5 31.4 Distillate oil 6.9 22.0 28.0 16.0 Heavy oil fraction 0.3 1.1 2.6 2.5

[0084] Comparing Examples 1 and 3, it is evident that recycling the circulating oil back to the feed inlet for co-pyrolysis with the waste plastics can further improve the yield of pyrolysis oil. This is likely because the presence of the circulating oil further increases the thermal conductivity of the material, reducing secondary reactions. Comparing the examples and comparative cases, it is clear that the pyrolysis process of this invention can achieve waste plastic pyrolysis at lower temperatures, while simultaneously increasing the yield of pyrolysis oil and reducing the yield of pyrolysis gas and semi-coke.

[0085] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A pyrolysis system, characterized in that, The system includes a feeding unit, a pyrolysis unit, a separation unit, and a heating unit; wherein, the feeding unit is used for drying and transporting waste plastics; the pyrolysis unit is used for pyrolyzing the waste plastics from the feeding unit and the circulating oil from the separation unit to obtain pyrolysis products; the separation unit is used for separating the pyrolysis products to obtain circulating oil, product oil, and pyrolysis gas; the heating unit is used for burning the pyrolysis gas to provide heat for the feeding unit and the pyrolysis unit; The feeding unit includes a material pit (1), a primary bucket elevator (2), a primary silo (3), a secondary bucket elevator (4), a secondary silo (5), and a discharge screw conveyor (6) connected in sequence. The discharge screw conveyor (6) is connected to the pyrolysis unit. The material pit (1) is used to store waste plastics, the primary bucket elevator (2) is used to transport the waste plastics in the material pit (1) to the primary silo (3); the secondary bucket elevator (4) is used to transport the waste plastics in the primary silo (3) to the secondary silo (5); and the discharge screw conveyor (6) is used to transport the waste plastics in the secondary silo (5) to the pyrolysis unit. The primary silo (3) and the secondary silo (5) are sealed storage devices with vents; the sealing prevents water vapor from spreading arbitrarily, while the vents are used to discharge water vapor generated during the transportation of waste plastics. Insulation jackets are provided outside the primary silo (3) and the secondary silo (5); The outer shells of the first-stage bucket elevator (2) and the second-stage bucket elevator (4) are provided with flue gas heating jackets, which are connected to the pyrolysis unit. The pyrolysis unit includes a horizontal pyrolysis reactor (7), wherein the horizontal pyrolysis reactor includes a reactor shell (71), a hollow stirring shaft (72), a spiral blade (73), and a sealing structure (74). The hollow stirring shaft (72) penetrates the reactor shell (71), and a hollow pipe for introducing high-temperature flue gas is provided in the hollow stirring shaft (72); the spiral blade (73) is provided on the hollow stirring shaft (72), and the sealing structure (74) is used to seal the connection between the hollow stirring shaft (72) and the reactor shell (71) and the inlet and outlet of the hollow pipe; The spiral blade (73) is provided with a vent hole, the diameter of which is ≤10mm; The separation unit includes a two-stage condensation separation device, wherein the first-stage separation device (8) is used to separate circulating oil with a boiling point ≥180℃, and the second-stage separation device (9) is used to separate pyrolysis gas to obtain product oil.

2. The pyrolysis system according to claim 1, wherein, The motor drive shafts of the first-stage bucket elevator (2) and the second-stage bucket elevator (4) are provided with cooling jackets, which are used to cool the motors. The primary bucket elevator (2) is sealed to the primary silo (3), and the secondary bucket elevator (4) is sealed to the primary silo (3) and the secondary silo (5) respectively.

3. The pyrolysis system according to claim 1, wherein, A stirring spiral is provided inside the secondary silo (5), and the bottom of the secondary silo (5) is a conical head with a cone angle of 30-120°.

4. The pyrolysis system according to claim 3, wherein, The cone angle of the conical head is 45-60°.

5. The pyrolysis system according to claim 1, wherein, The discharge screw conveyor (6) is selected from extruders and / or slag extruders and is located below the secondary silo (5).

6. The pyrolysis system according to claim 1, wherein, The reactor shell (71) is provided with a feed inlet, a discharge outlet and a gas outlet; wherein, the feed inlet is connected to the discharge screw conveyor (6) and is used to feed waste plastic; the discharge outlet is used to discharge the semi-coke generated in the pyrolysis reaction; and the gas outlet is connected to the separation unit and is used to transport the pyrolysis products generated in the pyrolysis reaction to the separation unit.

7. The pyrolysis system according to claim 1, wherein, The hollow stirring shaft (72) is coaxially arranged with the reactor shell (71); The coefficient of thermal expansion of the hollow stirring shaft (72) is greater than that of the reactor shell (71).

8. The pyrolysis system according to claim 1, wherein, The distance between the outermost edge of the spiral blade (73) and the reactor shell (71) is 5-20 mm.

9. The pyrolysis system according to claim 1, wherein, The helical spacing of the helical blades (73) is greater than the particle size of the waste plastic.

10. The pyrolysis system according to claim 1, wherein, The pyrolysis reactor also includes an expansion joint (75), which is disposed on the outside of the sealing structure (74).

11. The pyrolysis system according to any one of claims 1-10, wherein, The heating unit includes a gas boiler (10) and a fan (11); wherein, one end of the fan (11) is connected to the separation unit and the other end is connected to the gas boiler (10), and is used to transport the pyrolysis gas from the separation unit to the gas boiler (10); the gas boiler (10) is also connected to the pyrolysis reactor (7), the secondary bucket elevator (4) and the primary bucket elevator (2) in sequence, and the gas boiler (10) is used to burn the pyrolysis gas to obtain high-temperature flue gas, and transport the high-temperature flue gas in sequence to the pyrolysis reactor (7), the secondary bucket elevator (4) and the primary bucket elevator (2).

12. The pyrolysis system according to claim 11, wherein, The fan (11) is a variable frequency fan, wherein a pressure transmitter is provided between the variable frequency fan and the pyrolysis reactor (7), and the variable frequency fan and the pyrolysis reactor (7) are pressure-interlocked through the pressure transmitter.

13. A method for pyrolyzing waste plastics, characterized in that, The method includes the following steps: (1) Dry the waste plastic to obtain dried waste plastic; (2) The dried waste plastic is pyrolyzed to obtain pyrolysis products and semi-coke; (3) Separate the pyrolysis products to obtain circulating oil, product oil and pyrolysis gas; (4) Combust the pyrolysis gas to obtain high-temperature flue gas; wherein the high-temperature flue gas is returned to the heat source for drying and pyrolysis reactions in steps (1) and (2); The circulating oil is recycled back to step (2); The separation includes primary separation and two-stage separation. The pyrolysis products are first subjected to primary separation to obtain circulating oil; the remaining part is further subjected to secondary separation to obtain product oil and pyrolysis gas; wherein, the boiling point of the circulating oil is ≥180℃. The method is carried out in the pyrolysis system described in any one of claims 1-12.

14. The pyrolysis method according to claim 13, wherein, The drying process includes primary drying and secondary drying, wherein the drying temperatures for primary drying and secondary drying are each selected independently from 80-120℃.

15. The pyrolysis method according to claim 14, wherein, The drying temperatures for the primary and secondary drying stages are each individually selected from 100-110℃.

16. The pyrolysis method according to claim 13, wherein, The pyrolysis reaction temperature is 400-700℃, and the pyrolysis reaction time is 10-60 min.

17. The pyrolysis method according to claim 16, wherein, The pyrolysis reaction temperature is 450-550℃, and the pyrolysis reaction time is 30-50 min.

18. The pyrolysis method according to claim 13, wherein, At least a portion of the circulating oil is returned to the pyrolysis reaction; wherein the mass ratio of the circulating oil returned to the pyrolysis reaction to the waste plastic is 1:0.5-5.

19. The pyrolysis method according to claim 18, wherein, The mass ratio of the recycled oil to the waste plastics returned from the pyrolysis reaction is 1:0.5-2.

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